Cardiac rhythm management (CRM) devices such as pacers, cardioverters, defibrillators, cardiac resynchronization therapy (CRT) devices, as well as combination devices typically include flexible printed circuit boards. A printed circuit board is a laminate of dielectric layers sandwiching layers of conductive circuits. Conductive vias extend through the dielectric layers to electrically couple the circuits of different layers. The dielectric layers often have higher coefficients of expansion compared to the conductive materials used in the vias. The vias expand less in the presence of heat (e.g., heat from manufacturing processes or circuit operation) or moisture relative to the insulation material used in the dielectric layers. Moreover, the dielectric materials sometimes include fibers or the like. The dielectric layers expand more in directions orthogonal to these fibers and often expand in a direction substantially parallel to the vias.
Expansion of the dielectric layers applies stress along the less expansion prone vias. The stress is typically focused at the junctures between the vias and their contacts to the conductive layers on the circuit boards. Sufficient stress due to expansion of the dielectric material separates the vias from such conductive contacts. This can reduce circuit performance or even cause an electrical open circuit that can ruin the circuit board. Additionally, separation of the vias and contacts in manufacturing requires discarding of the affected circuit boards. This increases manufacturing costs. The present inventors have recognized an unmet need for reducing stress on conductive vias to avoid, for example, circuit board failure and to improve manufacturing quality.